The third World of Warcraft expansion pack has been officially unveiled as Cataclysm during BlizzCon 2009 in Anaheim, California.

Blizzard Entertainment's creative development VP Chris Metzen introduced the game's debut trailer to raucous applause from the assembled crowd of Blizzard fans, claiming the game "will very literally change the face of the world of Azeroth as you know it."

Notable amongst the expansion's additions are a new playable Horde race, the Goblins, as well as a new playable Alliance race, the werewolf-like Worgen. Unlike in previous expansion packs, the player level cap will be raised only 5, to 85, rather than by 10.

Apparently confirming early rumors, the trailer -- and Metzen's comment -- strongly suggested that the expansion will see many dramatically redesigned environments reflecting the occurrence of a catastrophic event, rather than simply adding new areas onto the existing game.

Other new mechanics include the Archaeology skill for characters, a leveling and achievement system for guilds, and ranked team multiplayer.